Petrogenesis of middle Triassic post-collisional granite from Jiefangyingzi area, southeast Inner Mongolia: Constraint on the Triassic tectonic evolution of the north margin of the Sino-Korean paleoplate

Zircon U–Pb dating and geochemical data are reported for the Jiefangyingzi and Yongshenghao granitic plutons from the Jiefangyingzi area to the northeast (NE) of Chifeng city, Inner Mongolia, with the objective of revealing the tectonic nature of the northern margin of the Sino-Korean paleoplate in early Mesozoic. Zircons from these granitic intrusions are euhedral and subeuhedral in shape with typical oscillatory zoning, indicating magmatic origin. The dating results indicate that these plutons formed in late middle Triassic (229 ± 2 Ma and 229 ± 1 Ma respectively), rather than in late Paleozoic, as previously thought. The Jiefangyingzi and Yongshegnhao granitic plutons are composed primarily of granodiorite and granite, with compositions of SiO2 = 63.23–68.91 wt.%, K2O = 3.06–4.51 wt.%, and A/CNK = 0.94–0.99. Chemically, they belong to the high-K calc-alkaline series and meta-aluminous I-type granites. Zircon εHf(t) values of both plutons range from +2.1 to +5.0 and +1.4 to +3.9, respectively, whereas the whole-rock εNd(t) values of Yongshenghao pluton range from −1.2 to −0.7, indicating the participation of depleted mantle material in their magmatic source. The petrological and geochemical characteristics suggest that these plutons are post-collisional granitoids. Combined with regional geological data, we conclude that these late middle Triassic granitoids formed during the transitional period from the post-collision setting to the post-orogenic extension setting after the collision between the Siberian and Sino-Korean paleoplates.

► Middle Triassic granites from the north margin of Sino-Korean paleoplate are found.
► The granites possess the petrological characteristics of post-collisional granitoid.
► There was participation of depleted mantle materials in their sources.
► They were formed after the collision between Siberian and Sino-Korean paleoplates.